1. Field of the Invention
The invention relates to the magnetic bubble memory devices.
2. Prior Art
Magnetic bubble memory devices for storing digital information are commercially available, for instance, from Intel Corporation. Generally, these devices employ a garnet substrate on which a magnetic garnet layer is formed in an epitaxial process. Permalloy members define localized magnetic fields under the influence of a rotating magnetic field causing the bubbles to move in the epitaxial layer. The permalloy members are fabricated over, and insulated from, the epitaxial layer. An intermediate layer of conductors, where needed, are also used for replicate gates, detectors, etc.
One failure mode in magnetic bubble memory devices occurs when a bubble slips or jumps, that is, when it does not move as intended. For example, a bubble, instead of following along a line of propagators, may jump to another line; or, instead of propagating from one chevron to the next, may slip backwards. The physical relationship between the permalloy members and the epitaxial layer, the magnetic field strength, and the shape of the permalloy members themselves, are some of the factors determining the reliability of the bubble propagation within the epitaxial layer. It is known, for instance, that by increasing the magnitude of the rotating magnetic field, more reliable propagation occurs, however, this requires additional power.
Other improvements have been suggested for improving bubble reliability. For example, in copending application, Ser. No. 483,914, filed Apr. 11, 1983, entitled "Method for Selecting Propagation Elements for Magnetic Bubble Memory", and assigned to the assignee of the present invention, differently shaped propagation elements are used for moving bubbles in opposite directions. This compensates for an asymmetry in crystal orientation in the epitaxial layer. Another suggestion has been to use different thicknesses of insulation between the permalloy elements and epitaxial layer to improve the magnetic coupling between the elements and the bubbles.
As will be seen, the present invention is directed to improving the reliability of bubble propagation in the epitaxial layer. Confinement channels are defined within the epitaxial layer to better confine the bubbles to predetermined propagation paths.